The chemical entity, 33-hydroxy-lup-20(29)-en-28-oic acid, generically known as betulinic acid and represented by the chemical formula (II),
is a naturally occurring pentacyclic triterpenoid (Journal of Applied Biomedicine, 2003, 1, 7-12) possessing useful biological properties such as anticancer, anti-inflammatory, antiviral, antiseptic, antimalarial, spermicidal, antimicrobial, antileshmanial, antihelmentic and antifeedent activities.However, amongst all the aforementioned activities, betulinic acid has been found particularly to exhibit anticancer and anti HIV activities (Journal of Medicinal and Aromatic Plant Sciences, 2002, 24, 1031-1037).
Earlier, betulinic acid was considered as a melanoma-specific cytotoxic agent, however, recent evidences indicate that it has a broad spectrum of activity against other types of cancer cells (IDrugs, 2004, 7(4), 359-373).
Betulinic acid has been selected by NCI, USA for Rapid Access to Intervention Development (RAID) programme. Betulinic acid has been shown to act through the induction of apoptosis irrespective of the cells p-53 and CD-95 status. Some experimental reports indicate that betulinic acid functions through the mitochondrial pathway. The pharmacokinetics and tissue distribution of betulinic acid has also been studied in CD-1 mice but a detailed investigation is required to find out its kinetic behavior (Biopharm. Drug Dispos., 1999, 20, 379-383). A recent study indicates that though betulinic acid has lower potency as compared to doxorubicin, but the former seems to be selective for tumor cells, since minimal toxicity against normal cells was observed (Cancer Letters, 2002, 175, 17-25). These findings and favorable therapeutic index, even at dose up to 500 mg/Kg body weight, have made betulinic acid a very promising candidate for the clinical treatment of various forms of cancer (Medicinal Research Reviews, 2004, 24(1), 90-114).
As a consequence of the promise betulinic acid holds for treatment of various types of cancer, research in the recent past has been directed towards synthesis and screening of new derivatives of the acid with a view of finding more potent compounds. A summary of the recent advances is given herein below:
At the outset, it might be mentioned that variations of substituents at positions 2, 3, 20 and 28 of betulinic acid molecule of formula (II), has been the subject matter of all research efforts to obtain potent lead compounds, viz, U.S. Pat. No. 6,018,847; U.S. Pat. No. 6,225,353; U.S. Pat. No. 6,369,109;U.S. Pat. No. 6,670,345; WO 98/51293; WO 98/51294; WO 02/16395; WO 02/091858; US 03/0181429; US03/0186945;U.S. Pat. No. 6,403,816.
Recently, isoxazole derivatives of betulinic acid have been reported as cytotoxic agents (Bioorganic Medicinal Chemistry Letters, 2003, 13, 3137-3140).
Even though, all the above mentioned reports collectively disclose a large number of betulinic acid derivatives, with a vast majority of them found to possess antitumor activity, however, due to various reasons they are not particularly good candidates, clinically as well as do not have the best of pharmacokinetic properties.
Of all the derivatives of betulinic acid discussed hereinbefore, findings from our laboratory show that one of the molecules disclosed in U.S. Pat. No. 6,403,816 and designated as MJ1098-RS of formula (III) exhibits good in vitro cytotoxicity in various cancer cell lines. U.S. Pat. No. 6,670,345 further discloses that compound of formula (III) also shows tumor reduction in murine xenograft models.

A need therefore, exists for new betulinic acid derivatives, which are not only potent, but also clinically safe and moreover, have better pharmacokinetic properties.
In our efforts to find molecules which are not only potent therapeutically but also acceptable clinically, we have found that substitutions at C-2 and C-3 positions of the betulinic acid of formula (II) with a heterocycle fused to the said positions, imparts the desired characteristics which forms the basis of the present invention.